Residents in northern NSW are being urged to prepare for what could be a first tropical cyclone in more than three decades.

Cyclone Alfred is expected to cross the coast sometime on Thursday.

Cyclone warnings have been issued from Bundaberg South to Grafton, just south of Yamba and Byron Bay.

BOM Manager of hazard preparedness Steven Bernasconi said in 1974 there were landslides which cut rail lines, and hundreds of people evacuated.

“That’s the sort of impact we are looking at,” he said.

“This is unusual for NSW hence the reason for the briefing. We don’t often have tropical cyclones watches and warnings in the NSW jurisdiction.”

The Hazards Near Me app is crucial for residents to download, he said.

SES Flood rescue crews are already in place.

Alfred is expected to intensify to a category two, with five being the strongest.

It’s armed with a triple threat, comprising 100km/h winds, waves in excess of eight metres and up to 300mm rain.

The last cyclone to hit NSW was Nancy in 1990.

Back in 1974 it was Cyclone Zoe.

Widespread heavy rain is expected from late on Wednesday, and will continue into the weekend.

Northern NSW can expect between 100 and 300mm of rain on Thursday and Friday, Bernasconi said.

“Today is about watching and preparing,” he said.

Cyclones are unusual in the north-east corner of NSW although the region is familiar with severe weather caused by east coast lows.

“For NSW, in particular the north-east of NSW, experiencing severe weather through east coast lows which have sometimes similar impacts to tropical cyclones, the impacts are well known,” Bernasconi said.

Coastal river catchments from the Tweed and Rous rivers in the north of NSW to the Camden Haven near Port Macquarie are on flood watch for moderate to major flooding.

Catchments are already wet and the flood risk will be exacerbated by high tides, the Bureau warns.

In tourist hotspot Byron Bay, white water is swallowing beaches.

Lifeguard Scott McCarthy said all of the beaches are closed, with waves “up to eight foot”.